| In China,the total area of carbonate rock accounts for about one-third of China's national land area.The importance of engineering problems in karst areas is increasingly prominent.At present,in karst area,there are more studies on the shield tunnel construction period,but less research on the operation period,especially the seismic response research on the shield tunnel.In addition,there are also few studies on the seismic response of the soil layer in the karst area.Therefore,it is necessary to study the seismic response of shield tunnels and soil layers in karst area during operation period.In the existing research,the simulation of karst caves is simplified into single karst caves,without considering the spatial distributi on of karst caves.In fact,the distribution of karst caves is very complicated.Therefore,how to simulate the distribution of karst caves closer to reality is of great significance for studying engineering problems in karst areas.Based on the above-mentioned problems,this article takes the Guangzhou Metro Line 9 project as the background and aims at the karst caves found below the bottom of the shield tunnel during the investigation and located outside the pretreatment range of the karst caves during the construction period.Then ignore the case where the caves are distributed in a beaded shape and the caves are connected,regard the karst caves as an approximately flat distribution,consider the influence of the random distribution of karst caves,and use numerical simulation methods to study the seismic response of shield tunnels and surrounding soil layers in the karst area during the operation period.And in order to predict whether the karst cave treatment principle in the current subway design can meet the safety requirements of the shield tunnel during the operation period.The main research work of this article is as follows:(1)Based on previous research results on the random distribution of karst caves,considering the distribution characteristics of the shape,size,density and location of karst caves in karst areas,the volume rate of karst caves and random parameters are introduced to simulate the random distribution of karst caves.(2)According to the simulation method of random distribution of karst caves,the distribution scheme of karst caves under different karst cave volume ratios was determined.And then use Midas GTS NX to establish a three-dimensional finite element model under the conditions of no cave and the volume rate of each cave.Then the seismic response of the shield tunnel under different seismic wave action modes in the operation period under the conditions of no cave and the volume ratio of each cave is compared and studied.At the same time,the seismic response of the soil layer around the shield tunnel under different seismic wave action modes in the operation period under the conditions of no cave and the volume ratio of each cave is compared and studied.After research and analysis,when the karst cave with a thickness gr eater than or equal to 2m at the bottom of the tunnel is not treated,the shield tunnel with a buried depth of about 7m,with the upper part in the sand layer and the lower part in the silt clay layer,has the following conclusions under the action of the earthquake:(1)When the seismic waves act in the horizontal,vertical,horizontal and vertical directions of the tunnel,the existence of karst caves at the bottom of the tunnel and changes in the volume ratio of the karst caves have no obvious effect on t he relative displacement and acceleration of the tunnel and the surrounding soil layers.The main stress of the tunnel segment shows that it increases first and then decreases with the increase of the volume ratio of the cave at the bottom of the tunnel.(2)According to the calculation results of this paper,when seismic waves act in the horizontal,vertical,and horizontal and vertical directions of the tunnel,the principle that Guangzhou Metro does not deal with karst caves with a thickness of 2m or more below the bottom of the tunnel can overall meet the safety requirements of shield tunnels during operation. |
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